The present invention relates to a switching power supply device that generates an internal supply voltage by subjecting an externally supplied supply voltage to voltage conversion. The present invention also relates to a microcomputer equipped with the switching power supply device.
In recent years, battery-driven devices such as electronic devices tend to have lower power consumption. In line with such a tendency, there is an increasing demand that the electronic devices operate on lower voltage. A switching power supply circuit described, for instance, in JP-A-2006-325281 is a switching power supply device for use with such electronic devices. This switching power supply device outputs a power supply output voltage VOUT through a DC/DC converter when a power supply input voltage VIN is activated. The configuration disclosed in JP-A-2006-325281 is such that a signal of a ring oscillator circuit, which is biased by the power supply input voltage VIN, turns on/off a switch of the DC/DC converter to raise the power supply output voltage VOUT without power supply output voltage feedback. According to JP-A-2006-325281, a comparator monitors the raised power supply output voltage VOUT. When the power supply output voltage VOUT is raised to a predetermined value, the switching power supply device switches from a non-feedback voltage increase operation based on the ring oscillator circuit to a feedback switching operation based on a PWM (Pulse Width Modulation) comparator, and exercises pulse width control in accordance with the power supply output voltage VOUT until a target value is reached.